Apparatus for making powder metal

ABSTRACT

An apparatus for making metal powder of ultra high purity which comprises a vessel defining a main collection chamber filled with an inert gas which serves as a heat transfer medium for effecting a cooling and solidification of molten metal particles injected therein. The apparatus further includes heat transfer conduits for cooling and recirculating the heat transfer gas through the main collection chamber and a refrigerated secondary collection chamber in which further cooling of the spherical powder particles is attained. Suitable controls are provided to assure appropriate pressure levels within the apparatus, whereby metal powders of optimum properties are produced.

United States Patent Di Giambattista et al.

[ 51 Apr.25,W72

[54] APPARATUS FOR MAKING POWDER METAL Mich. I [73] Assignee:Kelsey-Hayes Company 22 Filed: Feb. 19, 1910 [2]] App]. No.: 12,809

[52] US. Cl. ...266/34 R, 75/0.5 B, 26 4/12,

1 18/25 R [51] Int. Cl ..C2lc 7/00 [58] Field ofSearch ..24l/l6,l7;26,/5,11,12,

264/13, 14; 75/05 B, 0.5 AB, 0.5 BA, 0.5 BB, 0.5 BC, 0.5 C; 266/34 R;18/25 R [56] References Cited UNITED STATES PATENTS 3,549,140 12/1970Ingersoll ..266/ 3 4 R 3,457,336 7/l969 Harris ..264/l4 2,633,604 4/1953Allenetal. ..264/l4 Primary Examiner-Gerald A. Dost Attorney-Harness,Dickey & Pierce ABSTRACT An apparatus for making metal powder of ultrahigh purity which comprises a vessel defining a main collection chamberfilled with an inert gas which serves as a heat transfer medium foreffecting a cooling and solidification of molten metal particlesinjected'therein. The apparatus further includes heat transfer conduitsfor cooling and recirculating the heat transfer gas through the maincollection chamber and a refrigerated secondary collection chamber inwhich further cooling of the spherical powder particles is attained.Suitable controls are provided to assure appropriate pressure levelswithin the apparatus, whereby metal powders of optimum properties areproduced.

9 Claims, 7 Drawing Figures PATENTEBAPR 25 1972 3,658,131 1 SHEET 2 OF 4EEL- W715: 72/ A/ llzlkg f gi/z APPARATUS FOR MAKING POWDER METALBACKGROUND OF THE INVENTION The adoption of powder metallurgicaltechniques for fabricating components suitable for use under hightemperature conditions has occasioned an increasing demand for metallicpowders of heat-resistant alloys which are of high purity, enablingsubsequent compaction thereof into solid components approaching 100percent theoretical density. The deleterious effects of impurities, and,particularly oxides, on the high temperature properties of partsfabricated from such metal powders requires such powders to be preparedand handled under substantially dry inert atmospheres. Convention-ally,heat-resistant metal alloy powders are produced by gas atomization of amolten mass ofthe metal alloy in a hermetically sealed chamber, whichusually is filled with a suitable inert gas such as nitrogen, helium,argon, and mixtures thereof, for effecting a cooling and solidificationof the particles without any appreciable contamination thereof. In suchequipment, it is conventional to inject the molten atomized metalparticles into the upper end of a vessel defining the collection chamberand the particles become progressively cooled and solidify during theirgravitational drop to the bottom portion of the vessel where they areextracted in a manner so as to avoid any contamination.

There has been a continuing problem in the production of gas atomizedmetal powder employing inert gases as the heat transfer medium due tothe fixed volume of gas present in the collection chamber which quicklybecomes superheated upon initiation of the gas atomization processaccompanied by a corresponding rise in pressure, necessitating a ventingof the collection chamber to reduce the pressure. These foregoingfactors result in a decrease in the density of the inert gas at-'mosphere present in the collection chamber with a correspondingreduction in the heat transfer efficiency. This condition is a dynamicone causing continuous changes in the atomization environmentcontributing to unstable gas atomization conditions with attendantnozzle fouling and fluctuations in the particle size of the atomizedmass. In'some instances, still further problems are encountered such asa sintering and/or fusion of the molten particles, the production ofhollow powder particles incorporating entrapped inert gas in theinterior thereof, as well as excessive heat build up within the interiorof the collection chamber. In view of the fore'going, it is conventionalto limit the quantity of metal atomized in a single run to a relativelysmall amount to avoid one or more of the foregoing problems whichseriously detracts from the efficiency of the gas atomization process.

In accordance with the apparatus comprising the present invention,substantially long runs, permitting the atomization of relatively largeamounts of metal alloys, can be undertaken during which substantiallystable conditions are maintained within the apparatus so as to assureoptimum gas atomization of the melt and the attainment of metal powderparticles within the desired size range and purity.

SUMMARY OF THE INVENTION The benefits and advantages of the presentinvention are achieved by an apparatus which comprises an elongatedupright vessel defining a main or principal collection chamber which isformed at its upper end portion with a nozzle port through whichatomized molten metal particles are discharged and at its lower endportion with an outlet port through which the solidified metal particlesare extracted from the chamber. The principal collection chamber isfilled with an inert gas for effecting a cooling and solidification ofthe metal particles during their travel from the nozzle port toward theoutlet port. The heat absorbed by the inert gas is continuouslyextracted by cooling loops disposed in communication with the principalcollection chamber, thereby preventing heat saturation of the gas andavoidance of pressure increases requiring excessive venting of thecollection chamber. The apparatus further includes suitable deflectionmeans within the collection chamber for intercepting and deflecting anymolten metal which inadvertently may be discharged into the collectionchamber, thereby avoiding a contamination and fouling of the componentsand previously formed powder. The apparatus further includes controlmeans for continuously monitoring the pressure differential between themelt chamber and principal collection chamber and provides for acontrolled flow and venting of inert gas into and out of the collectionchamber to maintain optimum conditions. A secondary collection chamberdisposed in communication with the outlet port of the vessel is furtherprovided for receiving and effecting a further cooling of the powderparticles in response to their contact with a refrigerated inclinedramp.

Still other benefits and advantages of the apparatus comprising thepresent invention will become apparent upon a reading of the descriptionof the preferred embodiments taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view ofan apparatus constructed in accordance with the preferred embodiments ofthe present invention;

FIG. 2 is a magnified fragmentary side elevational view of the principalcollection chamber and melt chamber including sensing devices connectedto suitable controls for regulating the pressure differentialtherebetween;

FIG. 3 is a fragmentary somewhat schematic view of a typical gasatomization nozzle arrangement suitable for use in ef fectingatomization of molten metal;

FIG. 4 is an enlarged fragmentary vertical sectional view of the lowerportion of the main collection chamber illustrating the provision of adeflection cone above the outlet port thereof;

FIG. 5 is an enlarged fragmentary side elevational view of the secondarycollection chamber shown in FIG. 1;

FIG. 6 is a transverse cross sectional view of the secondary collectionchamber shown in FIG. 5 and taken along the line 66 thereof; and

FIG. 7 is a magnified vertical sectional view of one of the heattransfer loops on the main or principal collection chamber shown in FIG.1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in detail to thedrawings and as may be best seen in FIGS. 1 and 2, the apparatuscomprising the present invention is comprised of a series ofinterconnected vessels which define a vacuum melting chamber 10, a maincollection chamber 12, a secondary collection chamber 14 and acollection box 16. The upper vessel defining the melting chamber 10 isadapted to be equipped with suitable heating devices for melting acrucible of the metal to be atomized and incorporates pouring devicesfor pouring the melt at a controlled rate into a suitable gasatomization assembly. The melting chamber 10 is adapted to behermetically sealed in order that the heating of the metal charge to beatomized can be accomplished under vacuum or in the presence of a dryinert atmosphere so as to avoid any appreciable oxidation thereof.

The vessel defining the melting chamber 10 is connected by means of asuitable flange connection 18 to an upper section 20 of the elongatedvessel defining the main collection chamber 12. A gas nozzle atomizationassembly of any one of the various types well known in the art isadapted to be positioned at or adjacent to the flange connection 18whereby the metal charge, upon atomization, is discharged into the upperend portion of the main collection chamber in the form of fine-sizedmolten droplets which become solidified during the course of theirdownward travel. Typical of the various atomization nozzle assemblies isthe arrangement illustrated in FIG. 3 comprising a tundish 22 having adownwardly extending stem 24 which is formed with an orifice throughwhich a molten metal stream 26 is discharged and becomes fragmentized oratomized upon coming in contact with one or a plurality of high pressuregas streams 28 discharged from a series of nozzles 30 disposed incircumferentially spaced converging relationship. During an atomizationrun, the molten metal in the tundish is continuously replenished bymeans of a suitable crucible 31. It will be appreciated that alternativegas atomization arrangements, as well as other means for effecting afragmentation of the molten metal charge into droplets of the desiredsize, can be satisfactorily employed in lieu of the exemplary nozzlearrangement illustrated in FIG. 3.

The vessel defining the main collection chamber 12 is comprised of theupper section 20, an intermediate cylindrical section 32 and a lowerconical section 34, which are secured together so as to provide ahermetically sealed chamber. The downward and outward taper of the wallsof the upper conical section enables divergence of the atomized metalparticles 'without contacting the side walls of the vessel while stillin a molten state as they are injected into the main collection chamberat a point corresponding approximately to the position of the flangeconnection 18 defining a nozzle port. The molten metal particles areadapted to fall under the influence of gravity downwardly through theintermediate cylindrical section 32, during which travel they areprogressively cooled and eventually solidify into spherical particles ofthe desired size range. The solidified metal particles eventually comein contact with the inner surfaces of a lower conical section 34 and areguided downwardly thereby toward a flanged outlet port 36, through whichthey are discharged into the secondary collection chamber 14. To avoidany adverse coreaction between the hot metal particles and the vesseldefining the collection chamber, it is preferred to construct thesections 20, 32, and 34 of a stainless-type steel which resistsoxidation attack when exposed to an air atmosphere.

To further enhance a cooling of the atomized metal particles dischargedfrom the main collection chamber, the lower conical section 34 ispreferably cooled such as by means of a series of cooling coils 38disposed in heat conductive contact with the exterior surfaces thereoffor extracting heat therefrom by means of the circulation of a suitableheat transfer fluid through the cooling coils. For this purpose,conventional tap water, as well as any one of the well known fluidrefrigerants, can be employed for cooling the lower end portion of thecollection chamber.

In addition to the direct cooling of the walls of the collectionchamber, such as by means of the cooling coils 38, a further extractionof heat from the inert gas atmosphere within the main collection chamberis achieved by two heat transfer loops as best seen in FIGS. 1 and 7,which extend longitudinally of the intermediate cylindrical section 32and are disposed substantially diametrically opposite to each other.Each of the heat transfer loops is of an identical construction andoperation and, therefore, a detailed description ofone will suffice. Asshown in FIG. 1, a pair of flanged inlet ducts 40 are connected to theupper portion of the intermediate cylindrical section 32 and aredisposed in communication with the interior of the main collectionchamber in a region corresponding to the point at which the inert gas isat the highest temperature The inert gas atmosphere is adapted to bewithdrawn through the two inlet ducts into a U-shaped conduit 42, as maybe best seen in FIG. 7, which is provided with a conically shaped filter44 for extracting extremely fine-sized metallic powder particlesentrained in the gas. The filtered gas thereafter passes over thesurfaces of a tubular heat exchanger bundle 46 which is connected bymeans of supply lines 48 to a source of cooling fluid, which mayconveniently be water or any other of the well known refrigerants.

The withdrawal of the inert heat transfer gas from the upper portion ofthe main collection chamber, causing it to travel downwardly through thefilter and heat exchanger bundle, is achieved by a suction blowerassembly comprising a fan 50 and motor 52, which are axially mounted inthe lower portion of the U-shaped conduit 42, as best seen in FIG. 7.The cooled and filtered gas discharged from the blower assembly passesdownwardly and into outlet ducts 54, as shown in FIG. 1,

which are connected to the lower portion of the intermediate cylindricalsection 32 and are disposed in communication with the main collectionchamber into which the cooled gas is discharged. It will be apparentfrom the foregoing arrangement that the cooling loops effect acontinuous circulation and cooling of the inert heat transfer gas in adirection countercurrent to the flow of the metal powder. The suctionimparted by the blower assembly of each heat transfer loop serves toprovide a reduction in the pressure of the inert gas in the upperportion of the main collection chamber, which serves to further promotestabilization of the metal stream 26 from the tundish and avoidance oferratic operation and/or fouling of the atomization nozzle assembly.

In accordance with a further preferred structural feature of theapparatus comprising the present invention, a foraminous deflection cone56, as best seen in FIG. 4, is provided which is disposed in the lowerend portion of the main collection chamber adjacent to the flangedoutlet port 36. The deflection cone 56 is adapted to intercept andfragmentize and/or deflect a molten stream of metal moving downwardly asa result of an inadvertent malfunction of the gas nozzle atomizationassembly, thereby averting molten metal from directly entering thesecondary collection chamber 14, which might otherwise fuse with andagglomerate previously collected metal powder. The deflection cone 56 isformed so that during normal operation of the apparatus, the solidifiedmetal particles pass through the apertures therein and downwardly intothe secondary collection chamber. It will be further noted from thespecific arrangement as illustrated in FIG. 1 that the nozzle port 18,in which the gas atomization assembly is adapted to be mounted, isdisposed in direct vertical alignment with respect to the flanged outletport 36, above which the deflection cone is disposed. The deflectioncone can be positioned upwardly from the position as illustrated in FIG.4 in a region of the main collection chamber at which the metalparticles coming in contact therewith have sufficiently solidified so asnot to become appreciably deformed upon striking the mesh of thedeflection cone.

Upon passing through the deflection cone and outlet port 36 of the maincollection chamber, the solidified metal particles enter the secondarycollection chamber which is defined by an angularly inclined cylindricalvessel 58 which is provided with a flanged inlet port 60 in its upperend portion adapted to be sealingly connected to the flanged outlet port36. The lower or right-hand end of the vessel 58, as viewed in FIGS. 1and 5, is sealingly connected to a collection hopper 62 into which thecooled metallic powder is discharged. In accordance with a preferredconstruction, as shown in FIG. 5, the wall of the vessel 58 is providedwith a port 64 over which a light 66 is sealingly positioned so as toilluminate the interior of the secondary collection chamber 14, enablingvisual inspection of the collected powder through a suitable inspectionport 68 provided in a flanged hatch 70 sealingly affixed to the upperend of the vessel 58.

As is best seen in FIGS. 5 and 6, a refrigerated plate 72 is disposedwithin the interior of the cylindrical vessel 58 and is correspondinglyinclined downwardly toward the collection hopper 62. The upper portionof the plate is substantially flat and extends transversely of thecylindrical vessel 58 having the longitudinally extending edges thereofprovided with a suitable resilient gasket 74 forming a seal so as toprevent passage of particles downwardly between the longitudinal sideedges of the refrigerated plate. The refrigerated plate 72 extends forsubstantially the entire length of the cylindrical vessel 58 and isprovided with a wear plate 76 at the upper end portion thereof disposeddirectly beneath the inlet port 60. The wear plate 76 is comprised of anabrasion-resistant material which resists the wear resulting from theimpingement of the metal particles thereagainst. The refrigerated plate72, as best seen in FIG. 6, is provided with a plurality ofrefrigeration conduits 78 disposed in direct heat transfer relationshipwith the underside thereof through which a suitable refrigerant iscirculated as supplied from supply lines 80, which extend upwardlythrough the underside of the cylindrical vessel 58 through sealed ports.

In accordance with this arrangement, the solidified metal particlesentering the secondary collection chamber first strike the upper surfaceof the wear plate 76 and thereafter roll downwardly along the uppersurface of the refrigerated plate and in direct heat conductive contacttherewith, effecting a further cooling of the metal particles. Thecooled metal particles cascade off the lower edge of the refrigeratedplate and are accumulated in the collection hopper 62 which is connectedby means of a flexible bellows 82 to a flanged inlet port 84 on theupper surface of the collection box 16. The lower inner portion of theinlet port 84 is provided with a suitable removable flange or gate valve86 which, upon opening, effects a discharge of the collected metalpowder in the collection hopper so that it can be screened andclassified, and thereafter packed in hermetically sealed containersprior to removal from the collection box. During the removal of themetal powder from the collection box, the removable flange 86 can beclosed, thereby isolating the remainder of the system from the airatmosphere.

In accordance with the foregoing arrangement, gas atomization of themolten metal can be achieved providing substantially long runs withoutencountering overheating of the inert heat. exchange gas within the maincollection chamber, thereby avoiding unstable conditions resulting inthe production of metallic powder of less than optimum characteristics.In order to assure the maintenance of proper gas differentials betweenthe melting chamber and main collection chamber and a venting and/ormake-up of inert gas to maintain the proper pressure differential, acontrol system is provided for sensing the gas pressure present withinthe aforementioned chambers. As may be best seen in FIG. 2, the meltingchamber is provided with a presettable high-pressure vent valve 88 whichis adapted to discharge gas to the atmosphere whenever the internalpressure of the melting chamber exceeds a preset maximum limit.Ordinarily, the melting chamber is maintained under a positive pressurewithin the range of from about 2 to 3 psig. The actual pressure presentin the melting chamber can be visually determined by means of a pressuregauge 90. In ad dition, the melting chamber is further provided with apressure-sensing device 92 which may comprise a suitable pressure switchof the types well known in the art and which is electrically connectedto a ratio relay 94, an inert gas fill valve 96 and a low pressure inertgas bleed-in valve 98. Similarly, the interior of the main collectionchamber is provided with a pressure-sensing device 100, which iselectrically connected to the ratio relay 94 and to an inert gas fillvalve 102. The main collection chamber itself is disposed oncommunication with a venting system, as shown in FIG. 2, comprising acyclone-type separator 104 which is connected at its outlet to a vacuumangle valve 106, the outlet of which is connected to an automaticpressure control valve 108, which is electrically connected to the ratiorelay 94. The outlet side of the automatic pressure control valve isconnected to the inlet side of a pressure control blower 110, impartinga suction pressure to the outlet side of the automatic pressure valve,effecting a withdrawal of the inert gas atmosphere from the maincollection chamber, depending upon the position of the automatic controlvalve 108.

In operation, after the metal to be atomized has been charged into themelting chamber, the entire system is sealed and evacuated to a pressurepreferably below 2 X l0' mm Hg. It is usually preferred to effect amelting of the metal charge while the system is under a vacuumwhereafter prior to pouring, the system is backfilled with a suitableinert gas, such as argon, to a positive pressure of about 23 psig. Thisis accomplished by an actuation and opening of inert gas fill valves 96and 102. At this point, immediately prior to pouring of the molten metalinto the gas atomization assembly, the pressure in the melting chamberand main collection chamber is the same. Since a differential pressurebetween the melting chamber and main collection chamber is desirable toassure uniform operation of the atomization nozzle and stability of themetal stream being atomized, the ratio relay 94 is preset in order toprovide a predetermined pressure difierential such as, for example, I to2 psig between the melt chamber and main collection chamber.

Just prior to pouring, the pressure control blower 110 is energized andthe vacuum angle valve 106 is opened, whereby inert gas is withdrawnfrom the main collection chamber at a rate dependent on the position ofthe automatic pressure control valve 108 as controlled by the ratiorelay 94. Assuming that the initial backfilling of the melt chamber andmain collection chamber was made to a pressure of 3 psig and the ratiorelay was preset to provide a pressure differential of 2 psig, theventing system connnected to the main collection chamber will operate towithdraw inert gas from the main collection chamber so as to attainthese preset conditions. At the same time that the pressure controlblower is energized, pressurized inert gas is fed to the nozzles 30(FIG. 3) of the atomization assembly and cooling fluid is circulatedthrough the coil 38, heat transfer bundles 46 and refrigeration conduits78, and the axial fan assemblies in the cooling loops are operating tocirculate gas therethrough.

During initiation of the pour, the filling of the tundish 22 effects asealing between the melting chamber 10 and main collection chamber 12,whereafter additional inert gas is bled into the melting chamber by theactuation of the inert gas bleed-in valve 98 to maintain the meltchamber at the desired preset level, such as 3 psig, during the entirerun. During the continuance of the gas atomization of the melt, theincrease in temperature of the gas in the main collection chamber, aswell as the discharge of additional gas into the main collection chamberby the noules 30 of the gas atomizing assembly, tends to cause apressure build-up in the main collection chamber which is continuouslymonitored by the pressuresensing device 100 which signals the ratiorelay 94 which in turn adjusts the opening of the automatic pressurecontrol valve 108, whereby the proper venting of the interior of themain collection chamber occurs. During the continuation of theatomization of the melt, the inert gas is continuously circulatedthrough the two heat transfer loops disposed in communication with theinterior of the main collection chamber, thereby minimizing pressurebuild-up and similarly minimizing the amount'of inert gas being vented,while at the same time assuring the maintenance of a reasonable densityof the inert gas atmosphere so as to provide satisfactory cooling of themolten metal particles.

While it will be apparent that the invention herein disclosed is wellcalculated to fulfill the objects above stated, it will be appreciatedthat the invention is susceptible to modification, variation and changewithout departing from the spirit thereof.

We claim:

1. An apparatus for producing powdered metal comprising an elongatedupright vessel defining a main collection chamber, said vessel formed atits upper portion with a melt chamber and a noule port through whichatomized molten metal particles are discharged into said main chamber,said vessel formed at its lower portion with an outlet port throughwhich solidified metal particles are discharged from said main chamber,said main chamber filled with an inert gas for extracting heat from themolten metal particles effecting a solidification thereof during thecourse of their travel from said nozzle port toward said outlet port,cooling means disposed in communication with said main chamber forextracting heat from said gas and recirculating the cooled said gas backto said main chamber, and pressure control means for controlling thepressure of the gas in said main collection chamber within a preselectedrange and at a pressure below that within said melt chamber disposed onthe opposite side of said nozzle port.

2. The apparatus as defined in claim 1, wherein said cooling means areoperative for withdrawing gas from the upper portion of said maincollection chamber and for returning the cooled said gas to the lowerportion of said main collection chamber.

3. The apparatus as defined in claim 1, wherein at least a portion ofthe surface of said vessel is disposed in heat exchange contact with acooling medium for extracting heat from the vessel.

4. The apparatus as defined in claim 1, in which said nozzle port isdisposed in vertical alignment above the said outlet ort. p 5. Theapparatus as defined in claim 1, further including deflection meansdisposed in said main collection chamber beneath said nozzle port forintercepting and deflecting a molten metal stream inadvertentlydischarged through said nozzle port.

6. The apparatus as defined in claim 1, in which said cooling meanscomprises a conduit extending exteriorly of said vessel and having theends thereof disposed in communication with the upper and lowerportions, respectively, of said main collection chamber; heat exchangermeans disposed in said conduit and adapted to extract heat from said gaspassing in heat exchanging relationship relative thereto, and blowermeans for withdrawing gas from the upper portion of said main collectionchamber into said conduit and relative to said heat exchanger meanstherein and thereafter for discharging the cooled said gas back into thelower portion of said chamber.

7. The apparatus as defined in claim 1, further including a secondvessel defining a secondary collection chamber disposed in communicationwith said outlet port, said secondary collection chamber formed with amember having a downwardly inclined surface along which the metallicparticles are adapted to travel in heat transfer contact therewith, andrefrigeration means for extracting heat from said member.

8. The apparatus as defined in claim 7, further including a collectionhopper disposed in communication with the outlet end of said secondarycollection chamber for collecting the cooled metallic particlestherefrom.

9. The apparatus as defined in claim 1, wherein said pressure controlmeans include sensing means for sensing the pressure of said gas in saidmain collection chamber and in said melt chamber and adjustable valvemeans operable in response to said sensing means for controlling thequantity of said gas vented from said main collection chamber.

1. An apparatus for producing powdered metal comprising an elongatedupright vessel defining a main collection chamber, said vessel formed atits upper portion with a melt chamber and a nozzle port through whichatomized molten metal particles are discharged into said main chamber,said vessel formed at its lower portion with an outlet port throughwhich solidified metal particles are discharged from said main chamber,said main chamber filled with an inert gas for extracting heat from themolten metal particles effecting a solidification thereof during thecourse of their travel from said nozzle port toward said outlet port,cooling means disposed in communication with said main chamber forextracting heat from said gas and recirculating the cooled said gas backto said main chamber, and pressure control means for controlling thepressure of the gas in said main collection chamber within a preselectedrange and at a pressure below that within said melt chamber disposed onthe opposite side of said nozzle port.
 2. The apparatus as defined inclaim 1, wherein said cooling means are operative for withdrawing gasfrom the upper portion of said main collection chamber and for returningthe cooled said gas to the lower portion of said main collectionchamber.
 3. The apparatus as defined in claim 1, wherein at least aportion of the surface of said vessel is disposed in heat exchangecontact with a cooling medium for extracting heat from the vessel. 4.The apparatus as defined in claim 1, in which said nozzle port isdisposed in vertical alignment above the said outlet port.
 5. Theapparatus as defined in claim 1, further including deflection meansdisposed in said main collection chamber beneath said nozzle port forintercepting and deflecting a molten metal stream inadvertentlydischarged through said nozzle port.
 6. The apparatus as defined inclaim 1, in which said cooling means comprises a conduit extendingexteriorly of said vessel and having the ends thereof disposed incommunication with the upper and lower portions, respectively, of saidmain collection chamber; heat exchanger means disposed in said conduitand adapted to extract heat from said gas passing in heat exchangingrelationship relative thereto, and blower means for withdrawing gas fromthe upper portion of said main collection chamber into said conduit andrelative to said heat exchanger means therein and thereafter fordischarging the cooled said gas back into the lower portion of saidchamber.
 7. The apparatus as defined in claim 1, further including asecond vessel defining a secondary collection chamber disposed incommunication with said outlet port, said secondary collection chamberformed with a member having a downwardly inclined surface along whichthe metallic particles are adapted to travel in heat transfer contacttherewith, and refrigeration means for extracting heat from said member.8. The apparatus as defined in claim 7, further including a collectionhopper disposed in communication with the outlet end of said secondarycollection chamber for collecting the cooled metallic particlestherefrom.
 9. The apparatus as defined in claim 1, wherein said pressurecontrol means include sensing means for sensing the pressure of said gasin said main collection chamber and in said melt chamber and adjustablevalve means operable in response to said sensing means for controllingthe quantity of said gas vented from said main collection chamber.